The ejection seats that are currently being used in high performance military aircraft are inherently unstable in free flight and are subject to uncontrolled gyrations following separation from the ejection guide rails. Such gyrations create excessive dynamic loads on the seat occupant that can cause serious injury or death. Therefore, there is a need to provide ejection seats with stabilization control that is effective as soon after separation from the ejection guide rails as possible.
Currently, stabilization control is most commonly provided in the form of a drogue parachute. The parachute is deployed when sufficient aircraft tail clearance is assured to slow the seat and stabilize it for a long descent until the recovery parachute is deployed. The use of a drogue parachute for stabilization control has some serious drawbacks. In order to insure that the seat is clear of the aircraft before the drogue is deployed, the deployment is usually initiated after a fixed time delay following seat/rail separation. The time delay is preset and is based on the slowest anticipated ejection velocity and the highest anticipated air speed. This method of predetermining the time delay results in maximizing the delay between seat/rail separation and the deployment of the stabilization control. In general, any increase in the time between seat/rail separation and the deployment of stabilization control will increase the chances of the development of a divergent seat attitude and resulting serious problems in achieving subsequent recovery.
The use of a drogue parachute for stabilization control also has the disadvantage of increasing deceleration loads on the seat occupant. When the seat is ejected into a high dynamic pressure airstream, the combined deceleration load produced by the airstream and by the deployment of the drogue can be beyond human tolerance. For example, loads in excess of 25 g's are possible, and such loads are likely to be fatal. In order to avoid such excessive and dangerous loads on the occupant, drogue deployment must be delayed until the seat deceleration has decreased to a safe level. Like the delay necessary to insure clearance from the aircraft, the delay until a safe deceleration level has been achieved increases the potential for divergent seat attitude. This is particularly true when the seat is ejected where higher airstream velocities are present.
Recent developments in aircraft crew escape technology indicate that an active, rocket-powered seat attitude control system is feasible and would provide much better short term postejection stabilization than a drogue parachute. A major drawback associated with the use of rockets for stabilization is that rockets require propellant which increases the seat weight and is relatively difficult to stow within the limited space available. Most known ejection seats have the undesirable aerodynamic characteristic of a tendency to pitch forward because the center of pressure is below the center of mass. In a system that relies solely on rocket power to provide stabilization control, the pitching moment must be overcome by a component of rocket thrust, and the providing of such thrust increases the amount of propellant required.
The patent literature includes a number of different approaches to providing stabilization and control of ejection seats following ejection. Rocket-powered seat control is disclosed in U.S. Pat. Nos. 2,751,171, granted June 19, 1956, to J. Martin; 2,931,598, granted Apr. 5, 1960, to G. E. Sanctuary; 3,554,472, granted Jan. 12, 1971, to R. G. McIntyre et al; and 3,979,088, granted Sept. 7, 1976, to J. B. McCormick. Martin discloses a system in which a rocket is used in combination with a drogue parachute to slow the seat and prevent impact with the ground. In the system disclosed by Sanctuary, the seat is tilted back to reduce the aerodynamic drag of the seat and thereby control the rate of deceleration and prevent dangerous abrupt deceleration. A rocket mounted on the back of the seat below the center of gravity is fired to tilt the seat, and then a second rocket above the center of gravity is fired to oppose the tilting and stabilize the seat in its tilted position. In addition, fins having horizontal and vertical vanes are deployed above and behind the headrest to aid the second rocket in opposing tilting and stabilizing the position of the seat. McIntyre et al disclose a yaw control stabilizing rocket that is mounted on the upper portion of the back of the seat, that has a discharge opening directed downwardly and rearwardly, that is rotatably adjustable by means of a gyroscope, and that is telescopically stowed in the catapult barrel prior to deployment. McCormick discloses a control rocket that has an adjustable throat area to compensate for deviations in the seat-occupant mass center of gravity.
Means deployed by a drogue parachute for flying the ejection seat to a more favorable landing area is disclosed in U.S. Pat. Nos. 3,662,978, granted May 16, 1972, to R. H. Hollrock; 3,679,157, granted July 25, 1972, to R. A. Roberts et al; and 4,017,043, granted Apr. 12, 1977, to J. J. Barzda. Both Hollrock and Barzda disclose a system in which helicopter-type rotor blades are deployed to provide "gliding flight". The blades are stowed against the back of the seat and are pivotably connected to the top of the seat. During deployment, the blades first pivot upwardly and outwardly to a position generally normal to the back of the seat and then pivot further into a position above the seat. A pair of tail planes are also deployed by the drogue chute. The tail planes are pivotably connected to the opposite sides of the top of the seat, are adjacent to the lower portion of the sides of the seat when stowed, and pivot upwardly and rearwardly into their deployed position in which they extend upwardly and rearwardly from the seat. Hollrock states that the booms of the tail planes may serve as casings for the catapult system. Roberts et al disclose a system in which wing-like surfaces trailed by a boom ending in fins are deployed to extend rearwardly from the bottom portion of the back of the seat. The apparatus is pivotably connected to the seat and is stowed up against the back of the seat.
U.S. Pat. Nos. 2,829,850, granted Apr. 8, 1958, to I. H. Culver; and 4,261,535, granted Apr. 14, 1981, to D. E. Swanson, each disclose apparatus for stabilizing the ejection seat and reducing drag until the rate of deceleration of the seat has reduced to a level at which it is safe to deploy the drogue parachute. The Culver apparatus includes a boom that is deployed forwardly of the seat and vanes that are aerodynamically deployed to extend laterally from the sides of the seat. Swanson provides two vertical rows of inflatable air bags that are sequentially inflated by gas generators as the seat is ejected from the aircraft.
Apparatus for providing an ejection seat with yaw stabilization is disclosed in U.S. Pat. Nos. 4,319,723, granted Mar. 16, 1982, to E. R. Schultz; 4,470,565, granted Sept. 11, 1984, to T. J. Zenobi et al; and 4,480,806, granted Nov. 6, 1984, to J. W. Duncan. Schultz discloses apparatus for yaw stabilization prior to drogue deployment and during the burning phase of stabilization rockets. A vertical vane mounted on the upper portion of the back of the seat senses angular offset and extends drag paddles laterally to provide restoring moment. Zenobi et al disclose flag-shaped fins that are pivotably connected to the top portions of the opposite sides of the seat, and that are pivotably deployed to extend rearwardly from the lateral edges of the top of the seat to provide yaw stabilization apparently prior to deployment of a drogue. Duncan discloses fins mounted in the same manner as the fins of Zenobi et al that are pivotably deployed, aerodynamically by the airstream and positively by a mechanical apparatus, to provide yaw stabilization while the seat is being slowed by a drogue parachute.
The above patents and the prior art that is discussed and/or cited therein should be studied for the purpose of putting the present invention into proper perspective relative to the prior art.